The age-dependent decrease in creatine kinase and aldolase activities in human striated muscle is not caused by an accumulation of faulty proteins.

In human striated muscle obtained in surgery, an age-dependent decrease in aldolase and creatine kinase specific activities and an increase in DNA content per wet weight was found. In the group of the elderly (64-84 years), the enzymes decreased by 40-60% when compared with a group between 24 and 47 years old, while DNA content rose by a factor of 1.53 indicating loss of tissue water. Titration of aldolase and creatine kinase molecules by specific antibodies against aldolase A and creatine kinase MM isozymes, respectively, revealed very little accumulation of aldolase cross-reacting materials in the old age group (1.13 fold), and no accumulation of inactive creatine kinase molecules. Similar conclusions can be drawn from thermostability analyses of these two enzymes. The data do not support the view that accumulation of modified proteins due to random errors or to post-translational alternations is a general or causative phenomenon of aging in human muscle tissue.